Cirrus clouds play an important role in the Earth’s radiation budget due to their high frequency of occurrence, nonspherical ice crystal formations, and variability in scattering/absorption characteristics. Mostly, tropical cirrus clouds are considered greenhouse modulators. Thus, the parameterization of tropical cirrus clouds in terms of their microphysical properties and the corresponding radiative effects are highly important for climate studies. For characterizing the radiative properties of cirrus clouds, which depend on the size, shape, and number of ice crystals, knowledge of the extinction coefficient (σ) and optical depth (τ) is necessary. σ provides information needed for understanding the influence of the scatterers on the radiative budget, whereas τ gives an indication of the composition and thickness of the cloud. Extensive research on tropical cirrus clouds has been carried out by using ground-based lidar (GBL) and satellite-based lidar systems. The characteristics of tropical cirrus clouds derived by using the data from the GBL system over the tropical site Gadanki (13.5° N, 79.2° E), India, during 2010 are presented. Some of the results are compared with those obtained by us from satellite-based cloud–aerosol lidar with orthogonal polarization observations of the cloud–aerosol lidar and infrared pathfinder satellite observation mission. It is observed that there is a strong dependence on some of the physical properties, such as occurrence height, cloud temperature, and geometrical thickness, and on the microphysical parameters in terms of extinction coefficient and optical depth. The correlation of both σ and τ with temperature is also observed.

Cirrus clouds are mainly composed of ice crystals and are known to be the major natural contributors to radiative forcing in the Earth’s atmosphere system. Describing the formation and microphysical properties of cirrus clouds and their role in climate models remain a challenging study. Lidar is a unique instrument, which provides the information on the optical and microphysical properties of cirrus clouds with good spatial and temporal resolutions. In this study we present the microphysical properties of cirrus clouds and their temporal variability, obtained using the ground based dual polarisation lidar at the tropical station Gadanki (13.5&deg; N and 79.2&deg; E), India, during the period January2009 to March 2011. Using the method developed in house for deriving range dependent lidar ratio (LR), the lidar measurements are used for deriving the extinction coefficient and to obtain the nature of the scatterers present in the cloud. It is noted that lidar ratio plays an important role and its measurements indicate directly the type of the ice nucleating aerosol particles present in the cloud. The long term data obtained on the structure of the cirrus in this regard are useful in the climate modelling studies.

The cirrus clouds play an important role in the Earth’s radiation budget due to their high frequency of occurrence, non-spherical ice crystal formations, and variability in the scattering/absorption characteristics. Mostly, the tropical cirrus clouds are considered as greenhouse modulators. Thus the parameterization of tropical cirrus clouds in terms of the micro- physical properties and the corresponding radiative effects are highly important for the climate studies. For characterizing the radiative properties of cirrus clouds, which depend on the size, shape and number of the ice crystals, the knowledge of extinction coefficient (&sigma;) and optical depth (&tau;) are necessary. The σ provides information needed for understanding the influence of the scatterers on the radiative budget whereas the τ gives an indication on the composition and thickness of the cloud. Extensive research on the tropical cirrus clouds has been carried out by using a ground based and satellite based lidar systems. In this work, the characteristics of tropical cirrus cloud derived by using the data from the ground based lidar system over the tropical site Gadanki [13.5&deg;N, 79.2&deg;E], India during 2010 are presented. Some of the results are compared with those obtained by us from satellite based CALIOP lidar observations of the CALIPSO mission. It is observed that there is a strong dependence of the some of the physical properties such as occurrence height, cloud temperature and the geometrical thickness on the microphysical parameters in terms of extinction coefficient and optical depth. The correlation of both the σ and τ with temperature is also observed.

Cirrus clouds play a significant role in the Earths radiation budget. Therefore, knowledge of geometrical and optical properties of cirrus cloud is essential for the climate modeling. In this paper, the cirrus clouds microphysical and optical properties are made by using a ground based lidar measurements over an inland tropical station Gadanki (13.5&deg;N, 79.2&deg;E), Andhra Pradesh, India. The variation of cirrus microphysical and optical properties with mid cloud temperature is also studied. The cirrus clouds mean height is generally observed in the range of 9-17km with a peak occurrence at 13- 14km. The cirrus mid cloud temperature ranges from -81&deg;C to -46&deg;C. The cirrus geometrical thickness ranges from 0.9- 4.5km. During the cirrus occurrence days sub-visual, thin and dense cirrus were at 37.5%, 50% and 12.5% respectively. The monthly cirrus optical depth ranges from 0.01-0.47, but most (&lt;80%) of the cirrus have values less than 0.1. Optical depth shows a strong dependence with cirrus geometrical thickness and mid-cloud height. The monthly mean cirrus extinction ranges from 2.8E-06 to 8E-05 and depolarization ratio and lidar ratio varies from 0.13 to 0.77 and 2 to 52 sr respectively. A positive correlation exists for both optical depth and extinction with the mid-cloud temperature. The lidar ratio shows a scattered behavior with mid-cloud temperature.

Cirrus clouds have been identified as one of the atmospheric component which influence the radiative processes in the atmosphere and plays a key role in the Earth Radiation Budget. CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) is a joint NASA-CNES satellite mission designed to provide insight in understanding of the role of aerosols and clouds in the climate system. This paper reports the study on the variation of cirrus cloud optical properties of over the Indian sub - continent for a period of two years from January 2009 to December 2010, using cloud-aerosol lidar and infrared pathfinder satellite observations (Calipso). Indian Ocean and Indian continent is one of the regions where cirrus occurrence is maximum particularly during the monsoon periods. It is found that during the south-west monsoon periods there is a large cirrus cloud distribution over the southern Indian land masses. Also it is observed that the north-east monsoon periods had optical thick clouds hugging the coast line. The summer had large cloud formation in the Arabian Sea. It is also found that the land masses near to the sea had large cirrus presence. These cirrus clouds were of high altitude and optical depth. The dependence of cirrus cloud properties on cirrus cloud mid-cloud temperature and geometrical thickness are generally similar to the results derived from the ground-based lidar. However, the difference in macrophysical parameter variability shows the limits of space-borne-lidar and dissimilarities in regional climate variability and the nature and source of cloud nuclei in different geographical regions.

In recent years weather modification activities are being pursued in many countries through cloud seeding techniques to facilitate the increased and timely precipitation from the clouds. In order to induce and accelerate the precipitation process clouds are artificially seeded with suitable materials like silver iodide, sodium chloride or other hygroscopic materials. The success of cloud seeding can be predicted with confidence if the precipitation process involving aerosol, the ice water balance, water vapor content and size of the seeding material in relation to aerosol in the cloud is monitored in real time and optimized. A project on the enhancement of rain fall through cloud seeding is being implemented jointly with Kerala State Electricity Board Ltd. Trivandrum, Kerala, India at the catchment areas of the reservoir of one of the Hydro electric projects. The dual polarization lidar is being used to monitor and measure the microphysical properties, the extinction coefficient, size distribution and related parameters of the clouds. The lidar makes use of the Mie, Rayleigh and Raman scattering techniques for the various measurement proposed. The measurements with the dual polarization lidar as above are being carried out in real time to obtain the various parameters during cloud seeding operations. In this paper we present the details of the multi-wavelength dual polarization lidar being used and the methodology to monitor the various cloud parameters involved in the precipitation process. The necessary retrieval algorithms for deriving the microphysical properties of clouds, aerosols characteristics and water vapor profiles are incorporated as a software package working under Lab-view for online and off line analysis. Details on the simulation studies and the theoretical model developed in this regard for the optimization of various parameters are discussed.

There is growing interest in development of electro-optical systems capable of operation over long atmospheric distances in various atmospheric conditions. Some of these systems include laser communications, remote sensing, active and passive imaging, target tracking and designation and laser beam projection (directed energy) systems. As increasingly sophisticated electro-optical systems are used in the atmosphere, the character of the medium becomes important. Optical turbulence is one of the most important characteristics for propagation through the atmosphere. A single ended experimental setup using the Nd: YAG laser operating at 1064nm is used to study the temporal and spatial variations of refractive index structure parameter C<sub>n</sub><sup>2</sup> experimentally. In this paper we present the details of the experimental setup used for the measurement of range resolved refractive index structure parameter C<sub>n</sub><sup>2</sup>, over a two way slant 4.0 km free space laser path. Some of the results obtained using the experimental setup are presented and discussed.

It is well established that atmospheric aerosol play a vital role both directly and indirectly in the Earth’s radiation budget. The transport of anthropogenic aerosol from the urban locations increases the aerosol loading in the surrounding semi-urban regions. The solid waste disposal in the semi-urban regions also adds up to the total anthropogenic aerosol density in the region. In this study we investigated the aerosol characteristics in the Cheeryal Village (17.51&deg; N, 78.62&deg; E), which is located at a distance of about 20 Km in the suburbs of Hyderabad, India. A multi-wavelength laser radar was developed in-house and made operational at this location about 2 years back. The Nd:YAG laser (M/S Bright Solutions, Italy) based multi-wavelength lidar operates at 532 nm and 1064 nm with a pulse energy of 50uJ at both the wavelengths. The two wavelengths are generated coaxially with a pulse width of 10ns and the laser operates up to a PRF of 4 KHz. The receiver system consists of a 360 mm Newtonian optical telescope, 10 nm of interference filters and the Licel Gmbh, Germany make 250 MHz Photon Counting recorder. Lidar observations are conducted on relatively clear days during the one year period from January 2014 to December 2014. The aerosol extinction profiles are derived and compared with the model values corresponding to the Hyderabad urban region. It is observed that there is a heavy aerosol loading periodically at this location in relation to the sources of anthropogenic aerosols at Hyderabad urban area. The role of prevailing meteorological conditions, measured in real time, on the transport of the urban aerosol to this region is studied.

High altitude cirrus clouds are composed mainly of ice crystals with a variety of sizes and shapes. They have a large influence on Earth’s energy balance and global climate. Recent studies indicate that the formation, dissipation, life time, optical, and micro-physical properties are influenced by the dynamical conditions of the surrounding atmosphere like background aerosol, turbulence, etc. In this work, an attempt has been made to quantify some of these characteristics by using lidar and mesosphere–stratosphere–troposphere (MST) radar. Mie lidar and 53 MHz MST radar measurements made over 41 nights during the period 2009 to 2010 from the tropical station, Gadanki, India (13.5°N, 79.2°E). The optical and microphysical properties along with the structure and dynamics of the cirrus are presented as observed under different atmospheric conditions. The study reveals the manifestation of different forms of cirrus with a preferred altitude of formation in the 13 to 14 km altitude. There are considerable differences in the properties obtained among 2009 and 2010 showing significant anomalous behavior in 2010. The clouds observed during 2010 show relatively high asymmetry and large multiple scattering effects. The anomalies found during 2010 may be attributed to the turbulence noticed in the surrounding atmosphere. The results show a clear correlation between the crystal morphology in the clouds and the dynamical conditions of the prevailing atmosphere during the observational period.

Cirrus cloud measurements over the tropics are receiving much attention recently due to their role in the Earth's radiation budget. The interaction of water vapor and aerosols plays a major role in phase formation of cirrus clouds. Many factors control the ice supersaturation and microphysical properties in cirrus clouds and, as such, investigations on these properties of cirrus clouds are critical for proper understanding and simulating the climate. In this paper we report on the evolution, microphysical, and optical properties of cirrus clouds using the Mie LIDAR operation at the National Atmospheric Research Laboratory, Gadanki, India (13.5°N, 79.2°E), an inland tropical station. The occurrence statistics, height, optical depth, depolarization ratio of the cirrus clouds, and their relationship with ice nuclei concentration were investigated over 29 days of observation during the year 2002. Cirrus clouds with a base altitude as low as 8.4 km are observed during the month of January and clouds with a maximum top height of 17.1 km are observed during the month of May. The cirrus has a mean thickness of 2 km during the period of study. The LIDAR ratio varies from 30 to 36 sr during the summer days of observation and 25 to 31 sr during the winter days of observation. Depolarization values range from 0.1 to 0.58 during the period of observation. The ice nuclei concentration has been calculated using the De Motts equation. It is observed that during the monsoon months of June, July, and August, there appears to be an increase in the ice nuclei number concentration. From the depolarization data an attempt is made to derive the ice crystal orientation and their structure of the cirrus. Crystal structures such as thin plates, thick plates, regular hexagons, and hexagonal columns are observed in the study. From the observed crystal structure and ice nuclei concentration, the possible nucleation mechanism is suggested.

The optical properties of the cirrus clouds over a tropical inland station Gadanki, Tirupati were studied using a dual polarization lidar. The extinction coefficient, backscatter coefficient, optical depth and linear depolarization of the cirrus clouds are derived using the range dependent lidar ratio. This work reports the results obtained during the period of December 2006 to July 2007 which covers the three prominent seasons of the year in the Indian subcontinent. A variety of ice crystals like hexagonal thin plate, thick plate, columns, dendrites and aggregates were observed within the cloud. The geometrical and optical thicknesses of the clouds show strong seasonal variations. The occurrence frequency of thin cirrus clouds was found to be relatively high as compared to sub-visible and dense clouds. In almost all the cases, the cloud contains smaller ice crystals in the top part, larger crystals in the middle portion and mixed phase in the bottom portion. Compared to the winter and summer seasons the horizontally oriented ice crystals were observed more in monsoon period. The lidar ratio and linear depolarization ratio of the cirrus clouds were in the range of 3-40 sr and 0.1-1.5 respectively. The maximum linear depolarization ratio was observed for the clouds containing randomly oriented ice crystal with temperature below -80°C. The lidar ratio was found to be maximum for the thin plate crystals and minimum for thick clouds with horizontally oriented ice crystals. The extinction and backscattering coefficients of the clouds were in the range of 0.3x10-4 to 6 x10-4 m-1 and 0.12x10-4 to 3x10-4 m-1 sr-1 respectively during the observation period.

Laser radar (lidar) provides an excellent tool for characterizing the physical properties of atmospheric aerosols which play a very important role in modifying the radiative budget of the Earth's atmosphere. One of the important issues in lidar research is to derive accurate backscattering or extinction coefficient profiles required for understanding the basic mechanisms in the formation of aerosols and identifying their sources and sinks. Most of the inversion methods used for deriving the aerosol coefficients assume a range independent value for the extinction-to- backscattering ratio [lidar ratio, (LR)]. However, it is known that in a realistic atmosphere the value of LR is range dependent and varies with the physical and chemical properties of the aerosols. In this paper, we use a variant of widely applied Klett's method to obtain the range dependent LR values and derive the aerosol extinction profiles with good accuracy. We present the lidar derived aerosol extinction profiles in the upper troposphere and lower stratosphere corresponding to different seasons of the year of two distinctly different stations in the Indian subcontinent namely Trivandrum (8.33° N, 77° E), Kerala, India, a coastal station and Gadanki (13.5° N, 79.2° E), Tirupati, India an inland station. The range dependent LR is derived corresponding to different seasons of the year at the two stations. The lidar ratio, aerosol extinction coefficient (AEC), aerosol scattering ratio and aerosol optical depth show strong to medium seasonal variation at both the stations. The lidar ratio values at Trivandum vary in the range of 11-38 sr whereas the values range from 20-34 sr at Gadanki. AEC values at the Trivandum station vary from 7.9x10-6 to 6.9x10-5 m-1 and at Gadanki station the variation is from 1.27x10-5 to 6.9x10-5 m-1. It is proposed to use back-trajectory analysis to understand the sources of aerosol at the two stations.

Cirrus clouds have been identified as one of the most uncertain component in the atmospheric research. It is known that cirrus clouds modulate the earth's climate through direct and indirect modification of radiation. The role of cirrus clouds depends mainly
on their microphysical properties. To understand cirrus clouds better, we must observe and characterize their properties. In-situ observation of such clouds is a challenging experiment,
as the clouds are located at high altitudes. Active remote sensing method based on lidar can detect high and thin cirrus clouds with good spatial and temporal resolution. We present the result obtained on the microphysical properties of the cirrus clouds at two Tropical stations namely Gadhanki, Tirupati (13.50 N, 79.20 E), India and Trivandrum (13.50 N, 770 E) Kerala, India from the ground based pulsed Nd: YAG lidar systems installed at the stations. A variant
of the widely used Klett's lidar inversion method with range dependent scattering ratio is used for the present study for the retrieval of aerosol extinction and microphysical parameters of cirrus cloud.

The monsoon water cycle is the lifeline to over 60% of the world's population. The study on the behavioral change of Indian monsoon due to aerosol loading will help for the better understanding of Indian Monsoon. Aerosol system influences the atmosphere in two ways; it affects directly the radiation budget and indirectly provides condensation nuclei required for the clouds. The precipitation of the clouds in the monsoon season depends on the microphysical properties of the clouds. The effect of aerosol on cirrus clouds is being looked into through this work as an effort to study the role of aerosol on Indian Monsoon. The microphysical properties of high altitude clouds were obtained from the ground based lidar experiments at a low latitude station in the Indian subcontinent. Measurements during the Indian monsoon period from the inland station National Atmospheric Research Laboratory (NARL) Gadanki (13.5_ N, 79.2_ E), Tirupati, India were used for the investigation. The depolarization characteristics of the cirrus clouds were measured and the correlation between the depolarization and the precipitation characteristics were studied. The results obtained over a period of one year from January 1998 to December 1998 were presented.

Lidar has proven to be an effective instrument for obtaining high resolution profiles of atmospheric
aerosols. Deriving the optical properties of aerosols from the experimentally obtained lidar data is one of the most
interesting and challenging task for the atmospheric scientists. A few methods had been developed so far, to obtain the
quantitative profiles of extinction and backscattering coefficient of aerosols from the pulsed backscattering lidar
measurements. Most of the existing inversion methods assume a range independent value for the scattering ratio for
inverting the lidar signal even though it is known that the scattering ratio depends on the nature of aerosols and as such
range dependent. We used a modified Klett's method for the inversion of lidar signal that uses range dependent
scattering ratio (<i>s</i>) for the characterization of atmospheric aerosols. This method provides the constants k and <i>s</i> for all the altitude regions of the atmosphere and leads to derive the aerosol extinction profile for the lidar data. In this paper we
made a study on the errors involved in the extinction profiles derived using the range dependent scattering ratio and
discuss the approach in this regard to obtain the accurate extinction profiles.

This work reports the development and preliminary results of the Vibrational Raman lidar at a coastal station,
Trivandrum (8°33'N, 77°E). A Raman lidar technique for measuring atmospheric temperature and water vapor using
vibrational Raman spectra of N2 and H<sub>2</sub>O are discussed in detail. Interference filters at 607 and 660nm of 1nm band-
width are used in the Raman lidar channel. Nighttime temperature and water vapor profiles are obtained from 1-5km in
the lower atmosphere. Lidar water vapor profiles are in good agreement with the Regional Model data. The variation in
the temperature profiles may be due to the indirect aerosol effect in the lower atmosphere.

This paper discusses the various requirements of data acquisition and processing for Space Borne Lidar (Light Detection
and Ranging) system being developed in Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum for the
study of aerosols and clouds in the troposphere and lower stratosphere (0-40 km). The lidar system will be housed in a
polar orbiting satellite at an altitude of 600 km with a period of approximately 90 minutes providing global coverage.
The lidar operates by transmitting a laser pulse down (nadir looking) and receiving the backscatter returns from the
atmosphere. The laser source operates at dual wavelengths of 1064 and 532 nm with a pulse repetition rate of 5/10 Hz
with energy of 100 mJ. The receiving system consists of a 265 mm Fresnel lens telescope followed by backend optics
and detector systems. The data acquisition system uses three channels with two types of photo detectors, namely photo
multiplier tube and avalanche photo diode and operate either in analog (current) mode or discrete pulse (photon
counting) mode. The data acquisition system has to handle signals of wide dynamic range (4-5 decades) and acquire the
backscattered signal intensity with good spatial resolution. The analog channel will receive and digitize the 1064 nm
signal with 16 bit resolution and the photon counting channels will count the 532 nm signal upto 200 MHz rate. The data
backed up onboard is telemetered down to ground station during periods of visibility of satellite.

Laser Radar-Lidar has been established as a promising tool in the remote sensing of aerosols and cloud layers in the
atmosphere and in obtaining the altitude profiles of aerosol extinction coefficient. A variety of inversion methods have
been used to obtain the altitude profiles of extinction / backscattering coefficients of the aerosols from the Mie lidar
signals. Fernald's method which offers a general solution for the two component atmosphere involving aerosols and
molecules is widely used to obtain the altitude profile of aerosol extinction coefficient and backscattering coefficient.
This solution is most sensitive to the Boundary value at the calibration level and the aerosol extinction to backscattering
ratio. In this paper the sensitivity of the above mentioned parameters on the live lidar data obtained from the tropical
coastal station Trivandrum is investigated. In the following some numerical calculations are also carried out confining
the situation to lidar measurements in the horizontal direction in order to investigate the significance of extinction to
backscatter ratio and boundary value term in the solution for the two component lidar equation. This analysis is carried
out at various altitude regions under different turbidity conditions in order to obtain a profile for the aerosol extinction to
backscatter ratio for which the solution is less sensitive. Hence a new inversion method is proposed in the following
using this variable lidar ratio at each altitude while inverting the lidar signal so that the possible error can be minimized.

Lidar observations had been conducted to study the long-range transport of aerosol and their effect at tropical station,
Trivandrum during the period of 2001-2003. The presence of aerosol layers was observed on many days below about 5
km during the above period. The monthly values of aerosol extinction coefficient profile showed the presence of aerosol
layer in the height region up to about 5 km during the summer monsoon periods. However, during the Asian winter
monsoon period the aerosol layers were observed in the altitude region between 0.6 and 3 km. The extinction values
were high in the winter season and were typically found to be 3.4×10-4 m-1. The aerosol optical depth was calculated by
integrating the extinction values in the aerosol layer region and it was found to be between 0.2 and 0.35. The plausible
reasons for the formation of these layers were explained using the wind circulation pattern and air back trajectories.

Lidar techniques are based on the interaction of the laser beam with various constituents of the atmosphere like aerosols,
gas molecules etc. Various atmospheric conditions like temperature turbulence, refractive index variation, fog, rain etc.
really influence the transmission properties of the laser beam. An Imaging Lidar provides a 3-D Image of the targets like
clouds when used vertically up in the atmosphere or any terrestrial object on the ground when used horizontally. Various
image processing techniques are used to improve the image quality by using various mathematical models related to
atmospheric conditions. A portable IR Imaging lidar system has been designed and developed for imaging the terrestrial
targets during nighttime in complete dark conditions. The system is also being used for study of the structure of clouds in
the troposphere. The system mainly consists of a CW laser source operating in the IR region and a CCD array-imaging
device with zooming capability to cover the long range. The CCIR standard video output available from the CCD camera
is monitored by a high resolution monochrome monitor. The video output is digitized using a frame grabber board. The
digitized image is subjected to online and offline processing methods. The image signal depends on the integral response
of the laser source, reflection/scattering properties of the objects, atmospheric effects etc. Based on the image processing
methods needed to improve the quality of image under different atmospheric conditions, known a priori, an empirical
model is developed. This paper describes the imaging lidar system developed and the image processing.

LIDAR operates by transmitting light pulses of few nanoseconds width into the atmosphere and receiving signals
backscattered from different layers of aerosols and clouds from the atmosphere to derive vertical profiles of the physical
and optical properties with good spatial resolution. The Data Acquisition System (DAS) of the LIDAR has to handle
signals of wide dynamic range (of the order of 5 to 6 decades), and the data have to be sampled at high speeds (more
than 10 MSPS) to get spatial resolution of few metre. This results in large amount of data to be collected in a short
duration. The ground based Multiwavelength LIDAR built in Space Physics Laboratory, Vikram Sarabhai Space Centre,
Trivandrum is capable of operating at four wavelengths namely 1064, 532, 355 and 266 nm with a PRF of 1 to 20 Hz.
The LIDAR has been equipped with a computer controlled DAS. An Avalanche Photo Diode (APD) detector is used for
the detection of return signal from different layers of atmosphere in 1064 nm channel. The signal is continuous in nature
and is sampled and digitized at the required spatial resolution in the data acquisition window corresponding to the height
region of 0 to 45 km. The return signal which is having wide dynamic range is handled by two fast, 12 bit A/D
converters set to different full scale voltage ranges, and sampling upto 40 MSPS (corresponding to the range resolution
of few metre). The other channels, namely 532, 355 and 266 nm are detected by Photo Multiplier Tubes (PMT), which
have higher quantum efficiency at these wavelengths. The PMT output can be either continuous or discrete pulses
depending upon the region of probing. Thick layers like clouds and dust generate continuous signal whereas molecular
scattering from the higher altitude regions result in discrete signal pulses. The return signals are digitized using fast A/D
converters (upto 40 MSPS) as well as counted using fast photon counters. The photon counting channels are capable of
counting upto 200 MHz with a spatial resolution of few metres. The LIDAR data generated comes in burst mode and
gets transferred to computer system. Pulse to pulse averaging is done rangebinwise for SNR improvement. The range
normalized signal power is computed and the vertical profiles of backscatter and extinction coefficients are derived. This
paper describes the intricacies in the design of the high resolution DAS developed in-house to obtain the scientific data.
The optimization methodology used for handling the data is also described.

The design and development of the new Raman lidar of the Space Physics Laboratory, Vikram Sarabhai Space
Centre is presented here. This station is located at 8 degrees 33 minutes N, 77 degrees E in India. This lidar can monitor atmospheric temperature
(using Pure Rotational Raman Spectrum), aerosol extinction coefficient, water vapor profile and clouds. Advantages of
Pure Rotational Raman method over Vibrational Raman method are presented with the result obtained using Vibrational
Raman lidar. Optical layout of the lidar system, PRRS method and aerosol extinction measurements are described
briefly.

The cirrus clouds which are global in nature have been identified as one of the important constituents if the atmosphere.
They play a dual role in the earth radiation budget increasing the Earth's albedo while simultaneously decreasing the
emission of Infrared radiation to space. Tropical cirrus clouds come in a variety of forms ranging from optically thick
anvil cirrus closely associated with deep convection to optically thin cirrus layers frequently observed near the
tropopause. For better understanding of the formation, subsistence and dissipation of cirrus clouds extended studies are
necessary. From earlier investigations it is realized that the climatology of cirrus clouds is distinctly different at the low
latitude coastal station at the west coast of India. Some of the important characteristics of the cirrus clouds like time
history of formation and dissipation, geometrical and optical properties during the winter time have been investigated
using the ground based Mutiwavelength Lidar system designed and developed in house at the Space Physics Laboratory,
Vikram Sarabhai Space Centre, Trivandrum, India. The lidar provides a vertical resolution of 3.75m by making use of
the modified receiver electronics of the MWL system. The high resolution measurements have facilitated the study of the
fine internal structure, optical depth extinction coefficient and other parameters of importance of cirrus clouds. The
present paper describes lidar system and the results obtained over a period of one year covering all the seasons and the
peculiar characteristics of the cirrus during winter time at this coastal station.

Ground based lidars are widely used all over for the study of physical and optical properties of aerosols and clouds in the
atmosphere. The observed parameters on aerosols and clouds and their dependence on various meteorological parameters
are being studied using the ground based lidars at different laboratories. But the results obtained are mostly applicable to
local / regional particular to the lidar observation site. Space borne lidar is a unique system for observing the global
distribution of aerosols and clouds. It provides vertical profiles of the physical properties of the clouds and aerosols with
global coverage. Such data is useful for the validation of climate models and for process studies related to the climate
change and also for studies on transport of aerosols and pollutants. Retrieval of optical properties of clouds and aerosols
from the data obtained by the space borne lidar is very complex. Currently we are developing algorithms to produce
calibrated data products for space borne and ground based lidars. A software to produce simulated lidar backscatter
profiles applicable to space borne and ground based lidars has been developed, which generates data that matches the
expected performance of the lidars under varying conditions. Output simulated data includes 1064 nm total backscatter
profiles and 532 nm profiles for both the parallel and perpendicular polarization states. This paper describes the
methodology used for inverting the ground based lidar data and the strategy for validating the data which will be
obtained from the proposed space borne lidar to be launched by ISRO.

This paper reports the effects of third-order dispersion on the propagation of an optical soliton in an optical fiber: (1) the squeezing is nonuniform over the pulse, (2) a critical value of (beta) <SUB>3</SUB>, i.e., the third-order dispersion, governs the optimum range of squeezing as the soliton propagates along the fiber.

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